Science Buddies: "Ask an Expert"

I was given a Science project to where I need to design an experiment so I can calculate the efficiency of an energy transformation. I'm currently planning to do a electrical to thermal energy transformation but I am unaware of how I could measure this. I'm planning to design an experiment by measuring this energy transformation in a toaster. How could I possibly measure this energy transformation and then calculate the efficiency of the energy transformation?

Note: We are just designing the experiment not actually doing it

Hi DaRafster,
Based on your descriptions of the experiment, it sounds like you are going to need two type of measurements.

The first measurement is electrical which you can measure using a watt meter such as this:
https://www.amazon.com/gp/product/B0000 ... B00009MDBU

The second measurement is thermal, which gets a little trickier. Please take a look at this experiment where you are basically measuring the change in the temperature of the water for this measurement:
https://www.sciencebuddies.org/science- ... background

Hope this gives you an idea on how to structure your experiment.
Good Luck and please post again if there's anything else we can do to help.

Willey

Thanks a lot, the watt meter definitely helped, however I believe the calorimeter is best used when liquids like water is involved. I'm measuring the temperature of a toaster, I want to see how long it takes for the toaster to warm up over time so I can compare it to the amount of watts. So is the calorimeter still reliable for this experiment or should I use something else? If so, what should I use?

I am sorry to say that measuring the temperature of toaster is NOT going to be sufficient for the calculating energy conversion efficiency as you had described. To put it another way, the toaster is a thermal source and the work that it does (i.e. energy) needs to be captured and measured for your calculations. In order to capture this thermal energy, you need a medium such as water (or anything else that can retain the thermal energy, (gel,oil, etc...)) so that you can eventually measure the change and calculate the energy. (This is equivalent to having a battery on the electric side - you can measure the voltage of the battery but that is not the same measurement as the work that the battery did in your circuit.)

I hope that make sense.
Please post again if you have any questions.
Good Luck!
Willey

I apologize for asking so many questions, I still am not aware of what I should do. Are you saying I NEED to use something to retain the thermal energy such as water? It confuses me because I don't think water and a toaster would mix well together. If you were in my place, what would you change about this experiment to make it easier? I feel like this toaster temperature thing is complicated, perhaps I should change my experiment but still use this same energy transformation? Or is there another way to calculate the efficiency of this energy transformation? Again I apologize as I struggle in Science and I just seek help so I can do this project with the best possible effort.

Hi DaRafster,
There's no need to apologize. The entire purpose of this board is to answer questions so please keep them coming.

Back to your questions:
1. Are you saying I NEED to use something to retain the thermal energy such as water? Yes - because you need a way to measure energy on the thermal side.

2. It confuses me because I don't think water and a toaster would mix well together. If you were in my place, what would you change about this experiment to make it easier?

Yes, you are correct. Water and toaster doesn't mix as you suggested so you will need a container such as a cooking pot or beaker. To continue with this setup (and since we don't actually have to do it), I would suggest that you take apart the toaster to get to the heating element, setup a plate that you can rest the cooking pot filled with water on top of the heating element. At this point, you basically have a electric cook-top like the ones in a kitchen. With this setup, you should be able to measure changes in the temperature of the water with a thermometer as you apply the electrical energy.

As an alternate, you may be able to find some kind of heat pack / ice pack that can also absorb the thermal energy. In this setup, you might be able to put the pack directly into the toaster as a piece of "toast." (Unfortunately, the heat capacity of those packs may be difficult to find so you might need to setup a different experiment to determine it)

Again, no need to apologize for questions.
Good Luck and please post again if we can help with anything else.
Willey

Hi again, I just read this now and after reading it over a couple of times, it gave me the idea of instead of using a toaster, I should just use a kettle to boil water. Doing so will also use the same energy transformation plus water is involved! I just want to make sure this would work out. So would this me alright to do? If this is fine, do I still use the wattmeter and calorimeter? Again thanks for your help.

Hi DaRafster,
Yes, what you have proposed with using an electric kettle should work fine. (In a way, you are building a bigger version of a Calorimeter.) As we have discussed before, you will need a thermostat to measure the change in temperature in the volume of water that you are placing in the kettle. You may also need to seal the kettle so that the energy doesn't escape as steam to improve the accuracy of the setup.

And yes, you will still need to use a watt meter to measure the input energy (electrical). In order to calculate the efficiency of the energy transformation, you will need to know the input energy (electrical) and output energy (the absorbed thermal energy as measured by the change in water temp for a specific volume). The efficiency is then calculated by dividing the output energy by the input energy.

I hope that make sense.
Good Luck!
Willey

I'm currently about to finish my experiment but I'm wondering if I could calculate the efficiency of this energy transformation by converting the watts into joules. From what I've searched, 1 W = 1 J/s (joule per second). I just want to use the right vocabulary we have learned in this unit of energy transformation. I just need to know what units to use when dividing. Should I use joules or watts for electrical energy and °C, or joules for thermal energy?

*Volume of water is 1000mL

Hi DaRafster,
Please do be cautious about the unit of measurement that you are using. Watt is a unit of measurement for Power, not Energy. Electrical Energy is, typically, measured in Watt-Hour and is one of the unit of measurement on the Kill-a-Watt (it's the last button labelled KWH and stands for KiloWatt-Hour. 1 Watt-Hour = 3600 Joules. )

To calculate efficiency, you need to use the same unit for both number as efficiency is a unit-less value. (i.e. the units of the numerator and the denominator needs to cancel out when you divide them as part of your "dimensional analysis") In short, I would suggest using Joules for both the electrical energy and the thermal energy to make this easier.

You are doing great work thinking through the details of the experiment!
Good Luck and please keep the questions coming.

Willey

That makes much more sense now! However I'm just not sure how to make the temperature of the water into joules. How would you convert it?

This should be my last question and my experiment should be done!

Hi DaRafster,
The equation that you need to use to convert the temperature change back to Joule is described in equation 1 (Q = mc (T2 - T1)) of the Calorimeter experiment that we previously discussed. Please review the background section and I believe all of the information you need is there. (Just as an FYI, you have the option of either doing the calorimeter experiment to figure out the Specific heat capacity (c) of the water you are using or you can use the standard number out of a reference book. You also will NOT be using equation 2 since your kill-a-watt is doing the electrical power measurement for you.)

Willey

okay this SHOULD be the last question, it says c=for heat capacity, what would that mean it my experiment?

Hi,
In your experiment, c is the specific heat capacity of the water that you are heating up. Please refer to the first paragraph of the background section. I have posted the paragraph below.

"Specific heat capacity is the measure of the heat energy required to increase the temperature of a unit quantity of a substance by unit degree. For example, in units of grams, degrees Celsius, and joules, the specific heat capacity of water is 4.19 J/°C g. This means that it takes 4.19 joules (again, a joule is a measure of energy) to cause a temperature rise of 1.0 degrees Celsius in 1.0 grams (g) of water"

So, looking at the equation Q = mc (T2 - T1)) again for your experiment, you have:
m = mass of the water (you have to convert from ml to gram)
C= Specific Heat Capacity
(T2-T1) = change in temperature in Celsius

Since you have all of the terms, you can calculate Q (Joule) i.e. the thermal energy put into the water.
Good Luck!

Willey

Alright I'm officially done my experiment, I just want to thank you for your help! I'll be dropping by the math section soon as I have a math exam coming up.Thanks for your help!

That's great. You're welcome and best of luck with your math exam!